A resin composition for secondary coating of an optical fiber is a resin composition comprising: a photopolymerizable compound comprising a urethane (meth)acrylate having a number average molecular weight of 10000 or more and 40000 or less; and a photopolymerization initiator, the content of the urethane (meth)acrylate is 0.05 parts by mass or more and 15 parts by mass or less based on the total amount of the resin composition of 100 parts by mass, and the urethane (meth)acrylate is a reaction product of a polyol having a number average molecular weight of 1800 or more and 4500 or less, a diisocyanate, and a hydroxyl group-containing (meth)acrylate.

A resin composition for secondary coating of an optical fiber is a resin composition comprising: a photopolymerizable compound comprising a urethane (meth)acrylate having a number average molecular weight of 10000 or more and 40000 or less; and a photopolymerization initiator, the content of the urethane (meth)acrylate is 0.05 parts by mass or more and 15 parts by mass or less based on the total amount of the resin composition of 100 parts by mass, and the urethane (meth)acrylate is a reaction product of a polyol having a number average molecular weight of 1800 or more and 4500 or less, a diisocyanate, and a hydroxyl group-containing (meth)acrylate.

A method of manufacturing an optical fiber includes applying a curable resin composition containing a photopolymerization initiator so that an outer circumference of a glass fiber including a core and a cladding is coated, and forming a coating layer by radiating an ultraviolet ray to the curable resin composition and curing the curable resin composition. Forming the coating layer includes providing two or more non-radiation periods and intermittently radiating the ultraviolet ray three or more times so that a total time of the non-radiation periods is 0.010 seconds or more.

A method of manufacturing an optical fiber includes applying a curable resin composition containing a photopolymerization initiator so that an outer circumference of a glass fiber including a core and a cladding is coated, and forming a coating layer by radiating an ultraviolet ray to the curable resin composition and curing the curable resin composition. Forming the coating layer includes providing two or more non-radiation periods and intermittently radiating the ultraviolet ray three or more times so that a total time of the non-radiation periods is 0.010 seconds or more.

Embodiments of the current disclosure include small diameter single-mode optical fibers having gratings and methods of forming thereof. In some embodiments, methods of forming a small diameter single-mode optical fibers having gratings include providing an optical fiber having a core and cladding with a combined outer diameter of 100 μm to 125 μm and a coating having a thickness of less than or equal to 20 μm, wherein the coating comprises one of: (i) a high-modulus coating layer surrounding the cladding region; or (ii) a low-modulus coating layer surrounding the cladding region and a high-modulus coating layer surrounding the low-modulus coating layer; and exposing the core, through the coating, to a pattern of ultraviolet radiation to form an optical grating within the core.

A coating device includes: a fiber passage through which a glass fiber passes downward in a vertical direction; a first flow path which is a flow path allowing a primary resin to flow toward the fiber passage and includes a first branch path horizontally dividing the primary resin moving in a horizontal direction; a first temperature controller which is disposed along the first flow path and controls a temperature of the first flow path; a second flow path which is a flow path allowing a secondary resin to flow toward the fiber passage, includes a second branch path horizontally dividing the secondary resin moving in the horizontal direction, and is located below the first flow path; and a second temperature controller which is disposed along the second flow path and controls a temperature of the second flow path.

The optical fiber manufacturing method includes: a drawing step of drawing a glass fiber from an optical fiber base material with a melted tip; a passing step of passing the glass fiber through a fiber passage formed in a die; and a resin coating step of forming a resin layer on the outer periphery of the glass fiber by supplying a resin to the fiber passage through a flow path communicating with the fiber passage formed in the die. In the resin coating step, a temperature of the resin is controlled so that a supply pressure of the resin to the fiber passage becomes a value in a predetermined range.

A method for producing an optical fiber coated with a UV-curable resin material around a glass fiber includes: a step of applying the UV-curable resin material to the periphery of the glass fiber; a step of passing the glass fiber coated with the UV-curable resin material through an interior of a cylindrical body (illustrated with a quartz tube) capable of transmitting UV light; a step of irradiating UV light from outside the cylindrical body by using a light source (illustrated with a UV bulb) to cure the glass fiber and form a coating; and a step of controlling (illustrated with a power controller) a power input to the light source so that a cure extent of the coating is constant based on the illuminance of the UV light from the light source and the illuminance of the UV light transmitted through the cylindrical body.

A method for producing an optical fiber coated with a UV-curable resin material around a glass fiber includes: a step of applying the UV-curable resin material to the periphery of the glass fiber; a step of passing the glass fiber coated with the UV-curable resin material through an interior of a cylindrical body (illustrated with a quartz tube) capable of transmitting UV light; a step of irradiating UV light from outside the cylindrical body by using a light source (illustrated with a UV bulb) to cure the glass fiber and form a coating; and a step of controlling (illustrated with a power controller) a power input to the light source so that a cure extent of the coating is constant based on the illuminance of the UV light from the light source and the illuminance of the UV light transmitted through the cylindrical body.

A resin composition for secondary coating of an optical fiber is a resin composition comprising: a non-reactive urethane compound having a number average molecular weight of 10000 or more and 40000 or less, a photopolymerizable compound, and a photopolymerization initiator, wherein the content of the non-reactive urethane compound is 0.05 parts by mass or more and 10 parts by mass or less based on the total amount of the resin composition of 100 parts by mass, and the non-reactive urethane compound is a reaction product of a polyol having a number average molecular weight of 1800 or more and 4500 or less, a diisocyanate, and a compound having active hydrogen.